Plasma arc welding is generally accomplished by placing a welding torch adjacent a workpiece and directing an inert gas across the tip of an electrode provided in the torch body and onto a workpiece. The interaction of the inert gas and hot electrode forms a substantially constricted arc between the tip of the electrode and the workpiece.
In a typical plasma arc welding torch, the electrode is comprised of a refractory material and is mounted in the torch body in thermally and electrically insulated relation therewith. The electrode is enclosed by the torch body and an inert gas is directed through channel or channels in the torch body and across the tip of the electrode and exits the body along with the electric arc, through an opening in the forward portion of the body.
The inert gas acts upon the electric arc present between the electrode and the workpiece to constrict its shape to that of a substantially narrow column. The inert gas also provides the necessary atmosphere which allows for electrical transfer of the arc across the gap formed between the electrode and the workpiece. In addition, this inert gas (defined herein as a primary orifice gas) provides some shielding effect to the molten weld zone as well as penetration control of the arc, depending on the volume of orifice gas flowing through the torch body. However, typically, a greater shielding effect is required and is accomplished by directing additional inert gas (defined herein as shield gas) around the outer surface of the orifice member and across the orifice thereof to provide a total inert atmosphere at the weld zone. This additional inert (shield) gas may be the same type of inert gas and received from the same source as the orifice inert gas, if desired. Or, the additional inert (shield) gas may be a different or same gas received from a second inert gas source, if desired.
The quality of the constricted plasma arc column (formed by interaction of the inert orifice gas and the electric arc) depends on the type of inert gas used as the (orifice) gas, the tip configuration of the electrode, the size, shape and condition of the constricting orifice and the volume of orifice gas directed from the torch body.
In the present invention, a secondary inert gas (defined herein as a secondary orifice gas) is directed through a hollow electrode to coact with the arc to produce equivalent defect free welds in types and thicknesses of metals (ferrous and non-ferrous) with less total heat input per inch of weld (i.e. less current/voltage output and/or high travel speeds). The completed weld is more narrow with greater penetration at any given electrical current setting, thereby producing a more desirable Heat Affected Zone (HAZ) and greater ultimate tensile strength values.
The jet of secondary orifice gas channeled through the tubular electrode compliments the primary inert gas column channeled through the torch body to provide a "stiffer" arc less subject to becoming skewed and unequal in dimensional shape. This characteristic will aid in alleviating weld "cutting" defects caused by an asymmetrical arc and subsequent asymmetrical heating pattern at the weld joint.
The secondary orifice gas channeled through the electrode could be any one of the inert gases or semi-reactive gases or a mixture of two or more depending on the material being welded and the results desired.
It is, therefore, an object of the present invention to provide an improved plasma arc welding torch.
It is a further object of the present invention to provide such a plasma arc welding torch which utilizes a secondary inert gas in conjunction with a primary inert gas to provide a substantially "stiffer" arc from the electrode of the torch than a typical single inert gas provides.
It is yet a further object of the present invention to provide such a plasma arc welding torch with an electrode having a longitudinal passage therein through which the secondary inert gas is directed.